Enhanced sensitivity of the rat hepatoma cell to the daunorubicin analogue 4-demethoxydaunorubicin associated with induction of DNA damage

The H-35 rat hepatoma, a cell line which is relatively resistant to the classical anthracycline antibiotics such as Adriamycin [the concentration of drug which inhibits cell proliferation by 5090 (IC50) = 2.5 microM] and daunorubicin (IC50 of 0.5 microM), is markedly more sensitive to the 4-demethoxydaunorubicin derivative, idarubicin (IC50 of 0.025 microM). In contrast to daunorubicin, which has previously been shown to inhibit hepatoma cell proliferation in the absence of perceptible DNA cleavage, idarubicin induces concentration-dependent DNA damage which may account for its enhanced capacity to inhibit proliferation of the rat hepatoma. Free radical scavengers fail to interfere with inhibition of cell proliferation induced by idarubicin. Damage to the cell membrane or alterations in mitochondrial integrity do not appear to represent components of idarubicin toxicity in this tumor cell line. Inhibition of DNA synthesis by idarubicin parallels inhibition of cell growth; however, sensitivity of DNA synthesis to idarubicin is significantly less than that for cell proliferation (IC50 values of 0.5 microM and 0.025 microM, respectively). It is postulated that the antiproliferative effects of idarubicin in the H-35 rat hepatoma model may be a consequence of alterations in DNA integrity which ultimately result in the inhibition of cellular biosynthetic processes.